WRRCTMR No.56 Rotating Disc Sewage Treatment Systems for Suburban Developments and High-Density Resorts of Hawai'i

Abstract

Present experience with extended aeration plants in high density resort and suburban developments in Hawai'i has been generally unsatisfactory due to (1) inadequate system management resulting from insufficient manpower resources, and (2) high energy input required for aeration. A large scale pilot rotating disc unit was developed and field tested as a practical alternative to such extended aeration systems. A literature review on rotating disc systems provided information on the basic theory of operation, pilot plant sizing and configuration, pilot system operation and data-gathering techniques, and hydraulic and organic loading rates. Laboratory operation of a bench-scale (6-in. diameter discs) unit led to the conclusion that movement of solids within the unit would be a major problem. A large-scale pilot unit (2-ft diameter discs) was designed and fabricated to remove 85% BOD from 1000 gpd raw domestic sewage. The unit provides for primary settling, four-stage bio-disc biological treatment, final clarification and capacity for 50-day sludge storage and anaerobic digestion. The pilot unit has been installed and operated at the City and County of Honolulu's Pacific Palisades Wastewater Treatment Plant. Results from loading rates of 2.2 and 4.0 gpd/ft^2 are encouraging with 80-90% BOD and better than 90% SS removed. Further evaluation of the data as well as performance studies at other loading rates are continuing.